GSE PS3 (7-8)-8 - Motion

• 8a measuring distance and time for a moving object and using those values as well as the relationship s=d/t to calculate speed and graphically represent the data.
• 8b solving for any unknown in the expression s=d/t given values for the other two variables.
• 8c differentiating among speed, velocity and acceleration.

• Concepts contained in 8a:
  • measurement of distance and time
  • using a formula (s=d/t) to calculate speed
  • determining the units for such calculations
  • graphing position vs time for positive uniform motion.
  • meanings of “physics” words:
    • position vs distance traveled vs displacement [what’s important here?]
    • time (and change in time)
    • slope, both positive and negative
    • speed (and instantaneous vs average speed)
    • velocity (speed with direction) [I’d like to find a way for kids to develop a robust definition of velocity, for example lots of examples where speed is the same but velocity changes. I think this leads right away to 2D motion; it’s not interesting in the 1D case.]
  • understanding how to read a graph. At the most sophisticated level, identifying a change in time interval and the corresponding change in distance interval, and calculating the speed from those two numbers. Simpler, identifying starting point, time and distance values at any given point on the graph, etc. [a good application for CC Smart Graphs, if that’s ready in time]
• Concepts contained in 8b
  • using a formula (s=d/t) to calculate unknown quantities
  • using the formula many ways – solve for time or distance or speed
  • determining the units for such calculations
  • helpful corollary: understanding how the units match the formula
• Concepts contained in 8c:
  • Differentiating between uniform and accelerated motion.
  • Explaining the difference between acceleration, velocity, and speed. [I would put velocity vs. speed in 8a. This one is about acceleration vs. velocity. We need many graphical examples and practice using the language, for example “slowing down” being negative acceleration or deceleration.

• Measurement of lengths and times.
• Solving 3 variable equations
• Determining units
• Formal language: position, speed, distance, number line, origin, rate, average, slope, etc.
• Need for teachers to build on intuitive understanding (“we went 2 hours in the car at 50 mph, so we traveled X miles”)

• It’s hard to distinguish time (change from zero) from change in time (or distance)
• average speed vs. instantaneous speed
• quotes from “Making sense of secondary science”:
  • ...if speed is increasing, then acceleration is also increasing.
  • ...”going faster” is used in ambiguous ways, sometimes referring to the magnitude of the speed … and at other times referring to the speed increasing with time.
  • ...note here the importance of proportional reasoning…
  • children need to develop the language tools to describe motion appropriately… prior to developing an understanding of dynamical principles” (p. 155)
  • they generally regard the state of rest as fundamentally different from the state of motion.
  • It is widely accepted that pupils need to have opportunities to articulate their own views (p. 160)